1. Field of the Invention
This disclosure relates to catalyst compositions for producing hydrogen. More specifically, this disclosure relates to a catalyst composition for oxidative steam reformation of ethanol for producing hydrogen and the preparation method of the catalyst composition.
2. Description of Related Art
Energy is indispensable in our daily life. About 80% of energy relies on combustion of fossil fuels which will not last forever. Carbon dioxide and greenhouse gases generated during energy generation result in the risk of global warming. To solve the issue of environmental pollution, it is urgent to find a renewable, clean and sustainable new energy to replace the fossil fuels.
Hydrogen is an excellent energy source because it is an alternative energy with high electrical energy conversion efficiency. The quantity of heat energy generated from combustion of per kilogram of hydrogen is about 3 times of that of gasoline and 4.5 times of that of coke. The product of reacting hydrogen with oxygen is produced in the form of water with low-pollution to the environment. However, the volumetric energy density of hydrogen is low. To increase the energy density per volume unit, biofuels can be used to produce hydrogen. Furthermore, expensive transportation cost of hydrogen leads scientists to choose appropriate hydrogen sources as fuels of the new energy sources. At present, alternative hydrogen sources including hydrocarbon compounds such as methanol, ethanol, natural gas and light oil are used in majority. Among these, ethanol has many advantages such as higher fuel quality, cheaper price, easy access, easy storage, easy portability and higher energy density. Furthermore, ethanol can produce hydrogen at lower reaction temperature. As compared to the conventional gasoline fuel, the generated carbon dioxide is reduced by approximately 50% and the air pollutant such as nitrogen oxide, sulfur oxide and hydrocarbon compound is not produced.
Current technologies for converting ethanol into hydrogen include steam reforming of ethanol (SRE), partial oxidation of ethanol (POE), oxidative steam reforming of ethanol (OSRE) and others. Over the past decade, scientists have focused on the research that SRE can be operated at lower temperature. The chemical reaction equation for SRE is as follows.C2H5OH+3H2O→2CO2+6H2 ΔH0298=+347.4 kJ/mol
The SRE reaction belongs to a reaction having highest yield of hydrogen. However, since SRE is an endothermic reaction, the operation temperature is still high. In contrast, OSRE is an exothermic reaction and can react at relatively lower temperature, so it has become the research emphasis in the industry. The chemical reaction equation for OSRE is as follows.C2H5OH+½O2+2H2O→2CO2+5H2 ΔHR=−68 kJ/mol
In another aspect, according to previous studies, noble metals with high activities are used as catalytic active components for the catalytic reaction of hydrogen. The noble metals include rhodium (Rh), ruthenium (Ru), platinum (Pt), palladium (Pd), iridium (Ir) and the like. Because of relatively higher cost of the noble metals, alternative metals, such as iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu), are used as catalytic active components to reduce cost.
However, these catalytic active components adsorb on normal supporters like γ-Al2O3, SiO2, ZrO2, MgO and TiO2 with higher temperature of the conversion reaction of the catalyst composition which increases the breakage of carbon-carbon bonds as well as generates the depositions of carbon byproduct. It results in the loss of the activity of catalyst composition with reduced usable-life which results in the issues of cost reduction.
Hence, it is urgent to develop a catalyst composition with high energy conversion rate, reduced carbon deposition, and prolonged usable-life.